1. Field of the Invention
The present invention relates to a plastic case for a photographic film cassette, especially for a photographic film cassette having a port portion protruding radially outward from the peripheral surface of a cylindrical cassette shell.
2. Related Art
In a conventional ISO 135-type photographic film cassette, a roll of photographic film is contained in a cassette shell made of a metal sheet. The ISO 135 photographic film cassette is encased in a plastic case made especially for keeping the photographic film cassette and, thereafter, packed in a rectangular box (e.g., a cardboard box) for sale.
The conventional plastic case for the photographic film cassette is constituted of a case body having a closed bottom and a lid for tightly closing an open top of the case body. The case body and the lid are each formed from resins. The plastic case is intended to protect the photographic film from moisture, and is thus required to have a high moisture resistance or a low moisture permeability of not more than 5 to 10 mg/24 hours. Since the conventional photographic film cassette is substantially cylindrical except for a port portion forming a film passageway which protrudes slightly from the peripheral surface of the cassette shell, the conventional plastic case also has a fundamentally circular horizontal contour. Because tight-fitness of engagement between two plastic parts can be kept better in curves than straight portions, it has been relatively easy to tightly seal the conventional regular cylindrical plastic case by fitting the lid to the open top of the case body.
On the other hand, photographic film cassettes are disclosed, for example, in Japanese Patent Application Nos. 5-127317 and 5-150402, whose cassette shell is constituted of elements made from resins, and which can wind the entire length of photographic film thereinto and advance the film leader to the outside by rotating the spool of the cassette. This type of photographic film cassette has a different contour from conventional ones, as is shown, for example, in FIG. 16. This is mainly because the new type photographic film cassette 110 needs to have an elongated port portion 110b for shielding the photographic film from ambient light entering through a film passageway 110a, and also enabling the film leader to be advanced to the outside through the film passageway 110a.
Since the new type photographic film cassette does not have a regular cylindrical contour, larger unused spaces 120a and 120b would result if the new type photographic film cassette 110 is encased in the conventional regular cylindrical plastic case 120. That is, space efficiency of the plastic case would be low.
For the above described and other reasons, there have been known various shapes of cases for photographic film cassette. For example, Japanese Patent Application No. 3-176371 discloses rectangular and semi-cylindrical cases, for indicating the conditions of the photographic film encased therein, e.g., as to whether the photographic film has been exposed or not. Also, Japanese Utility Model Publication No. 3-48581 discloses a case having an oblong horizontal contour so as to hold a couple of photographic film cassettes therein.
However, because either of the above-mentioned known cases for the photograph film cassette includes at least a straight portion in their horizontal contour, and gaps tend to form more frequently in the straight portion than the curved portion, tight-fitness between the case body and the lid and hence moisture resistance of these known plastic cases is inevitably lowered, compared to the conventional regular cylindrical plastic case. To solve this problem, JPY No. 3-48581 suggests forming ribs integrally with the lid. However, such ribs may cause the lid to have sink marks in the engaging portion with the case body. Therefore, it is hard to obtain sufficient moisture resistance.